1. Field of the Invention
The invention is directed to a bulldozer having an electrically operated pitch control system wherein the hydraulic angling cylinders are automatically coupled to tank when the hydraulic pitch cylinder is extended or retracted.
2. Description of the Prior Art
Both wheeled and tracked tractors may be provided with a forwardly mounted bulldozer blade for pushing dirt and other material. Typically the blade is coupled to a blade linkage which in turn is coupled to the frame of the tractor. The blade linkage is pivotally coupled to the tractor. Hydraulic raise and lower cylinders extend between the blade linkage and the supporting frame of the tractor for raising and lowering the blade. The blade itself is coupled to the linkage by a spherical bearing. The bulldozer blade, in turn, can be angled to the right and left relative to the linkage by hydraulic angling cylinders. By angling the blade dirt and other material is deposited on a selected side of the tractor.
The fore and aft pitch of some bulldozer blades can also be adjusted. It is desirable to adjust the pitch of the blade for different operations and conditions. On utility bulldozers, the assignee of the present patent application has provided specialized three hole pinning links to adjust the pitch position or three different pitch links for three different pitch positions, see U.S. Pat. No. 5,507,352. The pitch of the bulldozer blade is adjusted by moving the top portion of the blade forward and backward relative to a lower spherical bearing. In addition, hydraulic cylinders have also been proposed to adjust blade pitch, see U.S. Pat. No. 3,900,073.